Touchscreen displays are able to detect a touch within the active or display area, such as detecting whether a finger is present pressing a fixed-image touchscreen button or detecting the presence and position of a finger on a larger touchscreen display. Some touchscreens can also detect the presence of elements other than a finger, such as a stylus used to generate a digital signature, select objects, or perform other functions on a touchscreen display.
Use of a touchscreen as part of a display allows an electronic device to change a display image, and to present different buttons, images, or other regions that can be selected, manipulated, or actuated by touch. Touchscreens can therefore provide an effective user interface for cell phones, GPS devices, personal digital assistants (PDAs), computers, ATM machines, and other devices.
Touchscreens use various technologies to sense touch from a finger or stylus, such as resistive, capacitive, infrared, and acoustic sensors. Resistive sensors rely on touch to cause two resistive elements overlapping the display to contact one another completing a resistive circuit, while capacitive sensors rely on the presence of a finger changing the capacitance detected by an array of elements overlaying the display device. Infrared and acoustic touchscreens similarly rely on a finger or stylus to interrupt infrared or acoustic waves across the screen, indicating the presence and position of a touch.
Capacitive and resistive touchscreens often use transparent conductors such as Indium tin oxide (ITO) or transparent conductive polymers such as PEDOT to form an array over the display image, so that the display image can be seen through the conductive elements used to sense touch. The size, shape, and patter of circuitry have an effect on the resolution and accuracy of the touchscreen, as well as on the visibility of the circuitry overlaying the display. Other materials, such as fine line metal elements are not optically transparent but rely on their small physical width to avoid being seen by a user.
One common application for touchscreen displays is presentation of keyboards, numeric keypads, and other input displays on mobile devices such as cellular telephones or “smart” phones. But, using a mobile device display typically no larger than about two inches by three inches to display a keyboard having over 26 keys results in a relatively small area per displayed key. Each key's corresponding touchscreen actuation area associated with each key is therefore also typically significantly smaller than a typical user's finger, making touch accuracy an important factor in efficient user input using such a keyboard.
For reasons such as this, a variety of touchscreen control algorithms have been employed to accurately detect and to correct sensed user input. These algorithms include features such as determining which key was most likely pressed when multiple keys are actuated at the same time, and automatic detection and correction of apparent keying errors such as misspelling words. Performance of algorithms such as these plays an important role in the perceived usability and efficiency of a touchscreen display keyboard implementation, and testing, comparison, and optimization of such algorithms is therefore desirable to provide a better user experience.